This invention relates to a valve and is particularly, although not exclusively, concerned with improvements in the type of valve used to prevent anything but air reaching a suction pump used in surgical or medical aspiration equipment.
Such equipment is used for a variety of purposes, such as the drainage of wounds or the collection of human milk. Typically it comprises a storage bottle for the fluid being drawn off and two tubes penetrating the lid of the bottle. One of the tubes opening to a lower position in the bottle leads e.g. to the wound being drained or can be connected to a human breast and the other tube, opening to a higher position in the bottle, leads to the low pressure side of an air pump. By displacing air out of the bottle body fluid is drawn into it. When the bottle is sufficiently filled the pump is stopped and the bottle sealed, if necessary being replaced by another one.
The utmost hygiene is, of course, vital in the use of such equipment, not only to prevent the transmission of disease between different patients using the same equipment, but to prevent escape into the environment, e.g. of a hospital ward, of micro-organisms from the output side of the pump. To quote from British Standard 4199: Part 2: 1968, "Surgical Suction Apparatus":
"When infective material is being aspirated, the inevitable bubbling and splashing in the collecting bottle create a bacterial aerosol which passes into the pump and often from its exhaust outlet into the air of the room".
Measures to protect the pump, discussed in the same British Standard, include an "air leak needle valve" and a filter. It is not herein suggested that a filter should be dispensed with, but the inadequacy of a filter alone to cope with the problem is discussed in the British Standard. Because a filter will become wet ". . . if the bottle becomes filled with froth, and is not immediately changed, fluid is sucked through the filter and into the pump".
By an"air leak needle valve" the British Standard is believed to refer to a float valve of the kind used to control a carburettor, i.e. a buoyant body supporting the needle will float up on liquid entering the valve chamber until the needle engages a valve seat to close the valve. Float valves can take a variety of other forms of which the commonest, perhaps, comprises a captive ball which floats up in its cage to shut an air intake in the presence of liquid. Such a float valve, incorporated in a breast pump, is exemplified in British Patent Specification No. 2 155 792A.
Such float valves do not solve the present problem. They will close in the presence of sufficient liquid, but will allow e.g. fine bubbles or an aerosol dispersion to pass through to the pump without closing. A filter between the valve and the pump may not be effective to prevent infective material being blown out of the pump exhaust.
Furthermore, the most effective and commonly used method of sterilisation is by autoclaving. Known float valves are not suited to be subjected to high sterilising temperatures without danger of rupture.